Catch rates of monkfish ( Lophius spp.) by lost tangle nets in the Cantabrian Sea (northern Spain)

Abstract

Commercial tangle nets used for capturing monkfish were employed in an experiment designed to study the fishing pattern by tangle nets that are lost at sea, a phenomenon commonly known as ‘ghost’ fishing. To simulate lost nets, 27 fleets of tangle nets were deployed on soft bottoms in the Cantabrian Sea shelf at depths between 117 and 135 m. Nets were recovered at intervals of 1–12 months and their catches recorded (composition, abundance, size, biomass, preservation state) in two trials, measuring seasonal changes in catch rates. A fleet of tangle nets was operated following commercial procedures next to the abandoned nets, providing simultaneous estimates of commercial catch rates. Monkfish ( Lophius budegassa and Lophius piscatorius) dominated the fish catches in abandoned tangle nets (81%). In summer–fall conditions, abandoned nets showed after 135 days catch rates similar to those simultaneously recorded for commercial nets (respectively, 0.18 and 0.22 specimens per 100 m of netting), but ceased to capture monkfish after 224 days. In spring–summer conditions, monkfish catches were negligible in abandoned experimental nets and lower in the commercial nets than in the previous trial. The pattern of extended catch rates observed in tangle nets abandoned in deep water differed from studies using abandoned gill and trammel nets in shallow waters, which typically cease to capture fish much sooner. Total monkfish catches by abandoned tangle nets were estimated through a cumulative catch model to be 17.7 kg (4.7 specimens) per 100 m of netting. Multiplying this value by the estimated number of tangle nets lost annually by the Cantabrian Sea fishing fleet, it was estimated that 18.1 t of monkfish are captured annually by abandoned nets. This represents 1.46% of the commercial landings of these species in the Cantabrian Sea.